Chinese Baijiu and Whisky | Encyclopedia MDPI

Chinese Baijiu and Whisky: History

Please note this is an old version of this entry, which may differ significantly from the current revision.

Subjects: Food Science & Technology

Contributor:

Qiuyu Zhang

Baijiu is a traditional spirit with high reputation in the Chinese community, and whisky, on the other hand, is a renowned spirit in Western culture, with both contributing a major proportion to the consumption and revenue in the global spirit market. Interestingly, starting with similar raw materials, such as grains, diverse production methods lead to different organoleptic profiles. In addition, such enormous attention they attract renders them as a crucial part in food and the related industry. Therefore, great efforts are made in improving product quality and optimizing production processes, such as flavor enhancement, facility development, and deep utilization of byproducts. Given the huge impacts and great involvements of these spirits in the general food industry, research focusing on either spirit is of referential significance for other relevant fields.

Chinese baijiu
whisky
food flavor
sensory analysis
functional food

1. Introduction

Spirits, or liquors, make up essential parts of the global alcoholic drink industry, or even the broader food industry. Specifically, spirits, such as whisky, brandy, rum, vodka, gin, tequila, and Chinese Baijiu, are of great popularity. Starting from different raw materials, such as grains (whisky, vodka, gin, Chinese Baijiu), fruits (brandy, rum, gin, tequila), vegetables (vodka, gin), and sugars (vodka, rum, gin), each spirit embraces unique production techniques leading to distinctive flavor profiles. Among them, whisky and baijiu share the most similarities in terms of raw materials (grains) and production processes (saccharification, fermentation, distillation, aging, and blending) and are both popular and symbolic alcoholic drinks in both Western and Eastern cultures.

Baijiu, also known as Chinese national liquor, is a distilled spirit originating from China. Embracing a history of 2000 years, baijiu enjoys a high reputation in the Chinese community. It ranks at the top on the global spirit-consuming list, with ~7.5 billion liters consumed in China in 2021 [1], and therefore, the baijiu industry, as a part of the food sector, plays a key role in the Chinese national economy. Made from diverse grains as raw materials, such as sorghum, corn, barley, and rice, and different production methods, baijiu is known for various aroma types, of which the symbolic ones are strong, light, sauce, rice, and mixed flavors [2]. Unlike most globally renowned alcoholic beverages, production of baijiu is featured with solid-state fermentation prior to distillation, with multi-microbes involved (semi-solid-state and liquid fermentation are also applied in some cases). Therefore, it attracts great research interest due to the complex liquor-making processes and the resultant intricate flavor profiles. Such studies have been reviewed thoroughly [2,3,4] to encourage further research on elucidating the correlations between baijiu flavors and the underlying microbial networks.

On the other side of the world, whisky, as a major global spirit, receives much attention, both commercially and academically. Reported with an annual consumption volume of ~6.0 billion liters globally in 2021 (Statista data), whisky has long been one of the most popular spirits worldwide. Similar to baijiu, whisky is known for different types, such as Scotch, Irish, American, Canadian, and Japanese whisky, resulting from different raw materials and/or production methods. On the other hand, however, uniqueness is noted especially for whisky flavors.

Both baijiu and whisky start with grains as raw materials and proceed with malting and saccharifying to produce fermentable sugar, followed by alcoholic fermentation. Distillation is conducted as the next step, yielding spirits, and final products are not released until aging for most types of baijiu and all whisky. However, major differences, especially flavors, are noticed between these two spirits. Critical processing steps, such as saccharification, fermentation, and aging, are essential in determining final flavors, and these are also where the variances occur for these two spirits. In addition, both products are made with such complex raw materials, as well as processing steps, that numerous compounds, contributing to the general properties of the spirits, are present. Among these, compounds of bio-functional values present in spirits are investigated as well, such as peptides, polysaccharides, and phenols. It may be controversial to study the health potentials of alcoholic beverages; however, such studies are necessary in that certain compounds in these spirits may mitigate, to various degrees, the side effects brought by ethanol. In addition, such investigation sheds light on wider ranges of studies focusing on functional food with biological values.

2. Volatile Compositions of Baijiu and Whisky

With diverse sensory profiles identified for both spirits, it becomes a crucial task to reveal the scientific nature, namely, volatile compositions, to thoroughly understand the flavor and sensory characteristics. Such knowledge may, therefore, play an instructive role in quality improvement during production. Similarities are observed for both baijiu and whisky based on volatile components, while differences in terms of quantities and compositions contribute greatly to their distinctive sensory characters. For better data interpretation, a heatmap (Figure 1) was hereby generated in terms of the occurrences of key aroma compounds reported in baijiu and whisky, while a correlation network (Figure 2) based on volatile compositions was proposed for both spirits [5,8,18,25,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49]. Data were obtained from various brands and styles of both spirits, with diverse sample extraction methods and identification methods applied in different studies. Such extraction methods include direct injection (DI), liquid–liquid extraction (LLE), liquid–liquid microextraction (LLME), solid-phase extraction (SPE), solid-phase microextraction (SPME), stir bar sorptive extraction (SBSE), and simultaneous distillation and extraction (SDE), and identification methods include GC-MS, GC-O-MS, GC-FID (flame ionization detector), GC × GC-TOFMS, GC-PFPD (pulsed flame photometric detection), GC-QTOF-MS, and UPLC-MS. For both spirits, factors such as alcohol strength, style, and production of origin, play crucial roles in volatile compositions and flavor profiles, making it complex to assess flavor similarities and differences. And, therefore, markers of significant representativeness are valuable for spirit comparison. Key aroma compounds, which are further identified in these studies by analyzing volatile concentrations and sensory contributions by means of the molecular sensory science approach, were included as such crucial markers for comparison due to their significant contributions to sensory properties (Figure 1). Specifically, the general methods involved in molecular sensory science study include identification and quantification of volatile compounds, aroma extract dilution analysis (AEDA) coupled with GC-O, aroma reconstitution, and omission tests coupled with sensory evaluation. And, such a comprehensive process renders it as a valid method for the identification of key aroma compounds, and therefore, comparisons accordingly help minimize the effects brought by other variables. Though both start with grains as raw materials, low similarities (~25%) in terms of key aroma compounds were observed in the baijiu and whisky ever reported, which may be explained by the diverse production methods of each spirit. On the other hand, a correlation network was proposed by analyzing volatile compositions available from the literature for both spirits (Figure 2). Surprisingly, certain styles of both spirits showed relevance, such as Bourbon whisky vs. most baijiu, and sauce-flavor baijiu vs. most whisky. To further specify the similarities and differences, detailed discussions are hereby made for common and crucial volatile compounds, including alcohols, esters, aldehydes, acids, and sulfur compounds.

Figure 1. Heatmap of the occurrences of key aroma compounds identified in baijiu and whisky.

Figure 2. Correlations among different styles of baijiu and whisky based on volatile compositions.

3. Instrumental Analysis Methods

Volatile detection is one of the most crucial methods for thoroughly understanding the flavor profiles of both baijiu and whisky. However, challenges are present due to the following reasons: a. the complex matrix various products offer; b. the generally broad and vague reference parameters for certain volatiles based on the literature, such as the retention index, thus potentially leaving out novel compounds; c. the relatively high detection thresholds of many instruments for trace compounds.

Many challenges were addressed throughout the development of instrumental analysis, thus rendering it a useful tool for decoding the chemical composition of different spirits. For instance, specific detection methods for sulfur-, nitrogen-, and phosphorous-containing volatiles are utilized, including the nitrogen chemiluminescence detector (NCD), nitrogen phosphorous detector (NPD), sulfur chemiluminescence detector (SCD), and flame photometric detector (FPD). In addition, other applicable extraction and detection methods are devised and summarized in Table 2.

Table 2. Extraction and detection methods for baijiu and whisky analysis.

Matrix	Pre-treatment Method	Analysis Methods	Compounds Analyzed	Flavor Contributions	References
Sauce-aroma baijiu	SPE, HPLC separation	UPLC-MS, NMR	6-(2-formyl-5-methyl-1H-pyrrol-1-yl)hexanoic acid, 2-hydroxymethyl-3,6-diethyl-5-methylpyrazine	Retronasal burnt aroma	[66,67]
	SBSE	UPLC-MS, GC-MS, GC-FPD, GC-NPD, GC-O,	Sulfur and nitrogen compounds, esters, ketones, aldehydes, amino acids	Important aroma compounds	[47,48]
	HS-SPME, LLE	GC-MS, GC-O, GC-FID, GC×GC-TOFMS	Sulfur compounds, esters, aldehydes, ketones, nitrogen compounds, alcohols, furans, acids	Important aroma compounds	[68]
Baijiu, general	derivatization	GC-MS	Non-volatile organic acids	Complex matrix effect	[38]
	LLE	GC-MS, GC×GC-TOFMS, GC×GC-SCD, AEDA, aroma reconstitution and omission experiments	3-Mercaptohexanol, 4-methyl-4-mercapto-2-pentanone	Tropical fruit	[69]
	derivatization	UPLC-MS/MS, UPLC-Q-TOFMS	Volatile thiols	Important aroma compounds, fruity character	[70]
	derivatization	UHPLC-HRMS	Carboxyl compounds		[71]
Feng-aroma baijiu	Direct injection	UHPLC-Q-Orbitrap, AEDA, aroma reconstitution and omission experiments	Acids, alcohols, aldehydes, ketones	Responsible for the honey aroma during aging	[18]
Light-aroma baijiu	DI, LLE, HS-SPME	GC-MS, GC-FID, GC-O, AEDA, aroma reconstitution and omission experiments	Esters, acids, alcohol, phenols, aldehydes, acetals, ketones, sulfur compounds, pyrazines	Key aroma compounds	[35,36,39]
Strong-aroma baijiu		GC-MS, FT-IR spectrometer	Esters, alcohols, acids	Important	[72]
Strong-aroma baijiu	HS-SPME, LLE	GC-MS/O, GC-MS	3-Methylindole	Mud-like off odor	[73]
Sesame-aroma baijiu	derivatization	LC-MS/MS, aroma reconstitution and omission experiments	Benzenemethanethiol	Important contribution to roasted aroma	[74]
	LLE, DI, VSLLME (vortex-assisted surfactant-enhanced emulsification liquid–liquid microextraction), derivatization	GC-MS, GC-FID, aroma reconstitution and omission experiments	Esters, alcohols, aromatics, phenols, furans	Aroma active compounds	[43]
	LLE, HS-SPME	GC×GC-TOFMS, GC-MS, GC-O, GC-FID, AEDA	Esters, alcohols, acids, aldehydes, acetals, ketones, sulfur and nitrogen compounds, heterocycles, alkanes, other aromatic compounds	Important aroma compounds	[8,40,41,42]
Herbaceous-aroma baijiu	HS-SPME, SPE, SBSE	GC×GC-TOFMS	Esters, alcohols, acids, aldehydes, ketones, terpenes, sulfides		[68]
Laobaigan-aroma baijiu	HS-SPME	GC×GC-SCD, AEDA	Volatile sulfur compounds	Aroma active trace compounds	[75]
Jian-aroma baijiu	LLE, HS-SPME	GC-O-MS/Osme	Esters, alcohols, acids, sulfur and nitrogen compounds, aldehydes, ketones	Aroma active compounds	[45]
Scotch malt whisky	LLE	MDGC-MS-O	E,Z-2,6-nonadienal, nonan-2-ol, 4-hepten-1-ol, E-2-nonenal, 1-octen-3-ol	Green note compounds	[65]
Scotch malt whisky		UV-HSI, hyperspectral imaging, SWIR-HSI, short-wave infra-red	Phenolic compounds	Responsible for smoky aroma	[76]
Scotch whisky	HS-SPME	GC-_ITMS (ion trap mass)	Esters, alcohols, acids, carbonyl compounds, monoterpenols, C₁₃ norisoprenoids, volatile phenols	Volatile compounds	[77]
American whisky		UHPLC-QTOF-MS/MS	Fatty acids, fatty acid lipids, phenolic compounds	Nonvolatiles	[78]
Tennessee whiskey	SAFE, SPE	GC-O, GC-MS, AEDA	Esters, ketones, alcohols, acids, aldehydes, sulfur compounds, furans, nitrogen compounds, alkanes,	Volatiles	[28]
Bourbon whisky		TD-HRGC-SIDA, (Two-dimensional high resolution) TD-HRGC-MS, GC-FID	Alcohols, alkanes, esters, ketones, aldehydes, phenols,	Potent volatiles	[32]
Whisky, general	HS, LLE, HS-SPME, HS Tenax full evaporation dynamic, SAFE	GC-MS, GC-FPD, GC-SCD, MDGC-MS, MDGC-ECD, MDGC-SCD, MDGC-NTD	Volatile sulfur compounds		[65]
	SAFE, HS-SPME, SBSE, SPME arrow	GC-MS, GC×GC-TOFMS	Esters, alcohols, nitrogen heterocyclic compounds, terpenes, acids, alkanes, aldehydes, phenols, lactones,	Volatiles	[31,34,79,80]
		FT-ICR-MS (Fourier transform ion cyclotron resonance), UHPLC-QTOF-MS/MS	Flavonols, oligolignols, fatty acids, polyphenol glycosides	Chemical signatures for barrel aging	[22]

Despite analytical technologies advancing greatly, a fixed and mature methodology is yet absent for most types of baijiu and whisky. And, such conditions in turn encourage further technical improvement of volatile analysis to expand the identification scope, as well as the detection level of aroma compounds, especially those present at trace levels, yet potentially crucial to sensory profiles.

For baijiu, various extraction methods coupled with qualitative and quantitative approaches were trialed and revealed the occurrence of more than 1, 900 flavor compounds. And, these extraction methods include direct injection (DI), liquid–liquid extraction (LLE), liquid–liquid microextraction (LLME), solid-phase extraction (SPE), solid-phase microextraction (SPME), stir bar sorptive extraction (SBSE), and simultaneous distillation and extraction (SDE). Similarly, a few of the abovementioned extraction methods are applied in whisky flavor analysis, such as SPME and LLE. On the other hand, however, solvent-assisted flavor evaporation (SAFE) was also reported as one of the techniques used during aroma profiling. Such a method may help with the extraction of non-volatile compounds or compounds with lower boiling points migrated from oak barrels into whisky.

The following analytical processes are also customized based on the detection requirements of various volatile groups and spirit types. Common techniques include gas chromatographic mass spectrometry (GC-MS), ultra-high-performance liquid chromatography (UPLC), and two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOF-MS). In analyzing particular compounds, such as compounds at trace levels, customized detection techniques are applied, such as nuclear magnetic resonance spectrometry (NMR), GC-NCD, GC-SCD, GC-NPD, GC-FPD, UPLC-high resolution mass spectrometry (UHPLC-HRMS), and UHPLC-quadrupole orbitrap HRMS (UHPLC-Q-Orbitrap HRMS).

Since volatile compositions are not in direct correlations with sensory characters due to the various thresholds and complex sensorial interactions between each compound, identifying the key aroma compounds contributing the crucial organoleptic properties is therefore of great importance. The molecular sensory approach, which incorporates instrumental analysis with sensory study, becomes increasingly popular for both baijiu and whisky research. Such a systematic methodology starts with the identification and quantification of volatile compounds, followed by recognizing their aroma contributions, via instrumental-coupled sensorial analysis. In identifying odor active values (OAVs), along with the conduction of aroma extract dilution analysis (AEDA), aroma omission, and reconstitution analysis, volatile compounds of crucial organoleptic contributions are identified for both spirits, which practically makes it possible for future potential flavor-targeted quality improvement.

This entry is adapted from the peer-reviewed paper 10.3390/foods12152841

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